1. Field of the Invention
This invention relates to an instrument for examining the human eye and more particularly to an instrument for examining the retina of the eye.
2. Description of the Prior Art
As a method of detecting abnormality of a retina, examining the angle of view field has been practiced and a perimeter is generally used. As an example of the construction of the perimeter, there is well-known the one which is provided with a fixation object centrally on a semispherical screen and in which a test spot projected upon the screen is moved in radial direction. In this method, an isopleth over 360.degree. is prepared by repeating the work of moving the spot light on the screen along a meridian, stopping the spot at a position whereat the subject exhibits a reaction and writing down that position on recording paper. The method of examining the view field now practiced has advanced from the examination of the limit of the visual recognition of a certain visible target, the width of such recognition, the degree or shape of the black spot to the expression of the degree or distribution of the photosensitivity of each region of the retina, the level of the sensitivity, etc. Where the minute portions of the retina are so discussed, the exact correspondence to the actual eye fundus becomes necessary. Heretofore, the relation with the region of the actual eye fundus has been inferred on an isopter having the examination result recorded on paper, but it is an inference to the last and assures no accuracy.
When examination is carried out, the subject is made to watch a fixation object to fix his line of vision and the examination is practised in such state. In that case, the portion of the retina which sees the fixation object is called the yellow spot which has the highest sensitivity on the retina. However, the region which gazes is not fixed where there is an eccentric fixation and it is possible that the subject looks aside from the fixation object and looks at the spot light during measurement, and it is desirable that this can be easily checked.
On the other hand, when developing a device for guiding the subjects line of vision by a retina camera disclosed in U.S. Pat. No. 4,068,932 (DOLS 2107788), the inventor has found that the technique is applicable to the measurement of the view field.